The present invention relates to therapeutic and prophylactic devices, and more particularly to devices for applying compressive pressures against a patient's limb.
It is known that the velocity of blood flow in a patient's extremities, particularly the legs markedly decreases during confinement of the patient. Such pooling or stasis of blood is particularly pronounced during surgery, immediately after surgery, and when the patient has been confined to bed for extended periods of time. It is also known that stasis of blood is a significant cause leading to the formation of thrombi in the patient's extremities, which may have a severe deleterious effect on the patient, including death. Additionally, in certain patients it is desirable to move fluid out of interstitial spaces in extremity tissues, in order to reduce swelling associated with edema in the extremities.
The problem of postoperative deep venous thrombosis (DVT) and prophylactic regimens in its management have been described by the National Institutes of Health Concensus Development Conference on Prevention of Venous Thrombosis and Pulmonary Embolism. Clearly it is a problem of major concern, and several prophylactic modalities are available to help prevent its occurrence.
Modalities which have been identified to be effective in the reduction of postoperative DVT have been categorized on the basis of their mechanism of action in either preventing the hypercoagulable state or preventing stasis. While anticoagulants have been shown to be effective, they carry a risk of bleeding and wound hematoma. On the other hand, complications have not been associated with use of compression modalities, such as intermittent pneumatic compression (IPC) disclosed in U.S. Pat. No. 4,013,069 incorporated herein by reference, and graduated compression stockings disclosed in U.S. Pat. No. 3,728,875, incorporated herein by reference.
Combinations of prophylactic modalities to act on more than one component of Virchow's Triad have been utilized to achieve increased prophylactic effectiveness. The addition of graduated elastic compression to low dose heparin reduces the incidence of DVT compared to low dose heparin alone. The addition of dihydroergotamine to low dose heparin has been demonstrated to be more effective in reducing DVT than low dose heparin alone. The finding that certain combination prophylactic regimens are more effective than single modality regimens was indicated in a recently published meta-analysis of the literature which also emphasized the finding that the combination of graduated compression stockings before or after use of intermittent pneumatic compression (IPC) was more effective than IPC alone.
The foundation of this conclusion involves the original series of Nicolaides on IPC prophylaxis which indicated that IPC was as effective as low dose heparin for the time it was applied; however, after IPC was discontinued prophylactic protection diminished. Nicolaides AN, Fernandes JF, Pollock AV. Intermittent sequential pneumatic compression of the legs in the prevention of venous stasis and postoperative deep venous thrombosis. Surgery; 87:69-76. 1980. Further work conducted by Nicolaides subsequently combined graduated elastic compression after IPC to provide a "continuity" of prophylaxis so that when IPC was discontinued, graduated elastic compression stockings were applied and worn through the remainder of hospital stay. This combination regimen utilizing graduated elastic compression before and after the application of IPC (but not during use of IPC) indicated a result comparable to that of low dose heparin. One point demonstrated in this work on IPC is that effective prophylaxis requires a "continuity" of prophylaxis for the entire time the patient is at risk.
The physical methods of prophylaxis, including graduated elastic compression and IPC, have long been considered to act by promoting venous blood flow and thereby reducing the stasis component of Virchow's Triad. The action of IPC has been demonstrated to significantly increase blood flow pulsatility and enhance blood clearance from the soleal sinuses, the axial veins and the valve sinuses. More recently, it has been indicated that IPC stimulates fibrinolytic activity and, in addition, enhances prostacyclin generation.
Therefore, the prophylactic effectiveness of IPC is thought to arise from potentially two actions, a reduction of venous stasis by increasing venous flow pulsatility and reducing the hypercoagulable state. The prophylactic effectiveness of graduated elastic compression stockings is thought to be due primarily to its reduction of venous stasis by increasing linear blood flow velocity.
Previous efficacy studies on IPC as applied to the surgical patient have not used graduated elastic compression stockings simultaneously with IPC, even though some studies have used stockings sequentially with IPC to provide an improved continuity of prophylaxis.